Natural Plant Toxins Aid Bees

Researchers studying the interaction between plants, pollinators and parasites report that in recent experiments, bees infected with a common intestinal parasite had reduced parasite levels in their guts after seven days if the bees also consumed natural toxins present in plant nectar.

In this early and most comprehensive study of its kind, researchers at the University of Massachusetts Amherst and Dartmouth College studied hundreds of eastern bumblebees, Bombus impatiens, and their intestinal parasite Crithidia bombi, using eight separate toxic chemicals, known as secondary metabolites, produced by plants to protect themselves against predators.

The eight chemicals studied were nicotine and anabasine found in the nectar of flowers in the tobacco family, caffeine from coffee and citrus nectar, amygdalin from almond nectar, aucubin and catalpol from turtlehead flowers, gallic acid from buckwheat nectar and thymol from basswood tree nectar.

They found that these chemicals in nectar reduced infection levels of the common bumblebee parasite by as much as 81 percent by seven days after infection.

UMass Amherst evolutionary ecologist Lynn Adler said, “We found that eating some of these compounds reduced pathogen load in the bumblebee’s gut, which not only may help the individual bees, but likely reduced the pathogen Crithidia spore load in their feces, which in turn should lead to a lower likelihood of transmitting the disease to other bees.”

She adds, “Because plants just sit there and can’t run away from things that want to eat them, they have evolved to be amazing chemists. They make biological compounds called secondary metabolites, which are chemicals not involved in growth or reproduction, to protect themselves. They are amazing in the diversity of what they can produce for protecting themselves or for attracting pollinators.”

Adler says results may have implications for growers who depend on pollinators, who may want to think about planting pollinator-friendly hedgerows and gardens containing plants that produce natural herbal remedies for some of the common parasites and diseases that ail bees and other pollinating insects.

“The more we look, the more we see that these compounds are in nectar and pollen too,” she adds. “With so many people looking at bee health these days, it’s taken a long time for us to realize that perhaps we should be paying attention to how floral secondary compounds mediate pollinator dynamics and their interactions with pathogens. Having bees consume these protective chemicals could be a natural treatment of the future.”

Commercial honeybee growers already use one such chemical, thymol, found in thyme plants, to treat mite infestations.